1. Field of the Invention
The present invention relates to photographic printers. In particular, the present invention relates to a photographic printer which automatically identifies and classifies film frames containing certain types of scenes.
2. Description of the Prior Art
Photographic printers typically produce photographic prints from photographic film originals (generally negatives). High intensity light is passed through the negative and imaged on photosensitive print paper. The photographic emulsion layers on the print paper are exposed and subsequently processed to produce a print of the scene contained in the negative.
A critical portion of a photographic printer is the exposure control, which controls the exposure of the photosensitive emulsion layers in order to ensure that the image on the print paper is properly exposed. The exposure control may utilize inputs from several different sources in order to determine the proper exposure.
Most automatic photographic printers measure the optical characteristics of the negatives and classify the negatives based upon these measurements. The types of negatives which can be automatically classified by optical measurements include (1) normal scenes, (2) subject density failures, (3) subject color failures, (4) color failures, (5) density failures, (6) snow scenes and beach/water scenes, (7) landscape scenes, (8) backlit scenes, (9) vertically oriented scenes, and (10) outdoor scenes. In most printers, the negatives containing normal scenes are printed using exposures derived from a method known as "integration-to-gray." With this method, it is assumed that the colors of the scene in the negative will integrate to gray over the print area, since the scene contains approximately equal amounts of red, green and blue.
While integration-to-gray results in proper exposure of the majority of all prints, the other types of scenes which can be automatically classified typically may not be correctly exposed by integration-to-gray. As a result, the exposure control of the photographic printer corrects or adjusts the exposures depending upon which type of scene is contained in the negative.
The frequency of particular types of scenes in an average population of negatives can vary significantly by season and geographical location. For example, during the winter months in the northern portions in the United States, a much larger number of snow scenes will be present than in other times of the year. Similarly, very few snow scenes are likely to be found in a population of negatives from the southern United States at any time during the year.
Because the population of negatives handled by a photofinisher will vary, it is advantageous to permit the photofinisher to adjust the sensitivity of the exposure control system to certain types of scenes. Thus, if the photofinisher has determined that the negative population will contain an abnormally high number of a particular type of scene, the photofinisher may desire to adjust the exposure control so that it is more sensitive to that particular type of scene.
Unfortunately, the classification of negatives into various types of scenes is a rather complex process in most photographic printers. The process typically involves various threshholds and other criteria for classifying negatives based upon the optical measurements. For example, in the photographic printer described in U.S. Pat. Nos. 4,168,120 and 4,168,121, sensitivity of a photographic printer to snow/beach negatives can be adjusted by the operator by varying a "SNRA" threshhold, which is a numerical value ranging from about 30 to about 70. A change in the SNRA threshhold results in a nonlinear change in the sensitivity of the exposure control to snow/beach type scenes, and also affects the sensitivity to others types of scenes in a converse fashion. As a result, the photofinisher, when changing the SNRA threshhold, must have a rather sophisticated understanding of the operation of the printer in order to achieve the desired change in sensitivity to snow/beach scenes.